The aid of this proposed research is to document, observationally, the emergence of emotion regulation during the second through fourth years of life; and to study individual differences and developmental pathways in emotional reactivity and regulation longitudinally, thereby elucidating underlying developmental mechanisms. Phenomena will be examined at both behavioral and physiological levels. Health Relatedness: Behavioral and emotional problems are among the most pervasive problems in society today. Failure to regulate emotions, as well as behavioral responses to emotions is a hallmark of psychopathology and other emotional problems. Research links behavioral and emotional problems to hormonal and immune system changes. There is also evidence to suggest that these connections between physiology and emotion dysregulation may represent causal mechanisms in both physical and mental disorders. Design & Methods: A group of 150 normally--developing children will be observed at 15, 24, 36 and 48 months of age. At each of these points, the children will be observed with their primary caregiver in emotion-electing situations to determine the flexibility and effectiveness of strategies used by children to regulate their negative emotional states. Cortisol levels will also be measured. Variables hypothesized to contribute to this development, such as parental functioning, child temperament, child/parent attachment, and parental socialization, will be measured. Structural equation modeling, stepwise regression, and ANOVAs will be used to evaluate the hypotheses.